According to recent studies, respiratory tract diseases including bronchial asthma and nasal hypersensitivity conditions (e.g., allergic rhinitis and vasomotor rhinitis) should be considered to be inflammatory diseases characterized by chronic inflammation of the respiratory tract mucosa in which a variety of phagocytes such as mast cells, eosinophils, and lymphocytes are involved, and also by sthenia in respiratory tract hypersensitivity induced by the inflammation. Thus, therapeutic agents for the respiratory tract diseases have gradually shifted from those containing bronchodilators, antiallergic agents, or anti-histamines to those containing anti-inflammatory agents, which reduce basophils and eosinophils present in the mucosal epithelium of the respiratory tract and lymphocytes and which inhibit release of cytokines from lymphocytes; release of mediators from basophils; secretion from glandular cells; vascular permeability; etc. Among such anti-inflammatory agents, steroid compounds exerting great therapeutic effects and less side effects have become of interest in terms of topical therapy, and heretofore, several steroid drugs that can be administered to the respiratory tract through inhalation have been developed.
However, when steroids, which are generally thought to exert a local anti-inflammatory activity, are administered to the respiratory tract, satisfactory site selectivity is not always attained. Steroids which are used at present still have unsatisfactory site selectivity, and safety of these drugs is not fully assured (e.g., grave side effect is induced by long-term administration).
Therefore, there is a demand for development of a steroid for use as a therapeutic agent for inflammatory respiratory tract diseases which exerts an excellent anti-inflammatory effect and which exerts high site selectivity and no systemic effect due to low bioavailability, when administered directly to the nasal cavity or to the respiratory tract via inhalation.